Once you are 18 you are entitled to vote in Local, National and European Elections. It is your opportunity to shape how the country is run. People who go forward for election (candidates) do so either as part of a political party or as an Independent.
Political parties have core values that they espouse and these generally entail them falling on the "left" (quite liberal in nature), "right" (distinctly conservative in nature) or centrist (i.e. somewhere general between the two). There are varying degrees of "left" and "right". In addition to their core values they also publish policy platforms on a whole range of issues in the run up to elections. These are the policies that they would seek to deliver should they enter government. Ireland has a history and tradition of coalition governments (i.e. two or more parties coming together to develop a majority) so it means that the policies they campaign on can get watered down in the negotiation of a Programme for Government.
Independent candidates are often former party members or people who have chosen to run on particular policy issues relevant to their own constituency i.e. save the local hospital or on a key environmental issue etc. Just like a political party, it is important to read up on what your candidate stands for before you give them your vote.